A commonly used technique for fabricating a catheter is to extrude a synthetic tubular sheath about an elongated, cylindrical mandrel and then to remove the mandrel from the sheath. Different size catheters for different invasive procedures are formed by using different diameter and different length mandrels. One example of a prior art catheter fabrication method is disclosed in U.S. Pat. No. 3,585,707 to Stevens. The disclosure of the '707 patent is incorporated herein by reference.
In accordance with the teaching of the Stevens patent, a flexible tubular catheter is constructed by extruding a plastic sheath onto a ductile wire mandrel. A braided layer of fine wire is tightly wound over the plastic coating and then a second plastic layer is extruded over the braided sheath. After a catheter sheath has been constructed in this fashion, the center wire mandrel is stretched to elongate the wire, thereby reducing its diameter and facilitating removal from the catheter sheath.
One technique that has developed in conjunction with the practice of the invention disclosed in the aforementioned '707 Patent is the use of a silver or nickel-silver coating on a copper wire mandrel. This coating facilitates removal of the catheter after it is extruded onto the mandrel. Experience with silver coated mandrels suggests that some of the coating may blister off the copper wire during the separation process. In addition, coating the wire mandrel increases the cost of fabricating the catheter.
Another disadvantage of the method described in Stevens is that a piece of the catheter must be removed from each end of the mandrel prior to mandrel separation, reducing the yield.